↑ In prime. Once I decide what to do with the ornamental panel on the front, the screw holes will be filled and covered over. The panel could be raised ½" or so to add LEDs behind it or it could be laminated to add strength.

Next will be a line for a GTO 8 that I have laying around. I'll probably use it for a computer sub but I might sell it. Then, when the SA-15 I ordered comes in, a line for it. If it works out well, I'll sell it, remove the seat from my truck and put two X-15s in a permanently mounted t-line.

Re: JBL GTO 10 in ¼ Wave T-Line

You don't have to do that but I wanted the wire to enter the cabinet at the back and in order to do that, it had to pass through the line. A transmission line is essentially one long port and the airflow through it is intense, so a wire running across it could introduce turbulence or possible some noise, neither of which I wanted.

Re: JBL GTO 10 in ¼ Wave T-Line

Originally Posted by Spooney

How do you go about designing one of these and what parameters in a driver would one look for to find a good t line driver?

I guess they didnt want my post with outside link to be read on here but if you are wondering about 1/4 wave tlines and how to build one and select good woofers to use for one based off of ts parameters just google "quarter wave tline tutorial" and you will see a nice thread on another car audio forum that explains everything simply and effectively.

Re: JBL GTO 10 in ¼ Wave T-Line

Originally Posted by 98GCLimited

I guess they didnt want my post with outside link to be read on here but if you are wondering about 1/4 wave tlines and how to build one and select good woofers to use for one based off of ts parameters just google "quarter wave tline tutorial" and you will see a nice thread on another car audio forum that explains everything simply and effectively.

Re: JBL GTO 10 in ¼ Wave T-Line

Like 98GC said, there are some really good tutorials on ¼ wave t-lines.

I'll go over the basics here though.

Any speaker will do well in a transmission line but those that do best have a Qts below .4 and a Qms below 7. The box is designed using only the Fs & Sd of the driver and the speed of sound, which is 1130 feet per second.

Fs is the resonant frequency of the driver. In the case above, that's 30hz.
Sd is the effective piston area of the driver. In the case above (can't remember exactly) that is ~56.75²".

To calculate the line length: 1130/30= 37.66' ←That's the length of a 30hz sine wave, but we're building a ¼ wave line so 37.66/4= 9.42' or, 9.5' to make things easy. This isn't brain surgery and slight variations won't be audible.

So what we have to do now is stuff a 9½' long by 56.75²" "port" into the cabin of a vehicle. The one above is 49" gross width and approx 14"H X 14"D. It has one 180° turn and one 90° turn.

From what I've read, there are about as many different ways to design a transmission line as there are people to ask... so do some due diligence before you start and decide what makes the most sense to you.

Save the difficulty in designing them, transmission lines are the loudest and best sounding woofer boxes you can build. They perform well across the widest frequency band and extend as far as one octave below their tuning frequency while still maintaining an above -3dB output.

Also, you don't have to stick to the Fs of the driver when building one. For instance, if you want a 40dB boost, you can put the same driver above in a line tuned to 40hz and you'll still get good performance at the frequency you want enhanced. I haven't done this but I would imagine that the only drawback would be that the driver would probably fall off at a steeper slope on the low end than if it were in a box tuned to Fs. That, of course, is just speculation as I haven't seen one modeled and I'm still in the learning process with these boxes.

Another benefit to transmission lines is that they're extraordinarily efficient. I had the one above in a local car audio shop connected to one side of a Lepia 20x2 mini amp (which actually does about 11wpc) and at 37hz the ceiling tiles started to reverberate. It's getting 1000 watts in my truck but in truth, as little as 250 watts has done well.

And once more to clarify... I'm still in the learning phase with these boxes so please don't take my claims about performance as the end all be all. The formulas I shared are correct but the performance characteristics have not been modeled on an RTA. At least, not by me... yet.

Re: JBL GTO 10 in ¼ Wave T-Line

Have you stuffed the Tline with fibre fill etc or left it open ? often fancied building a Tline for my JBL GT3-10 but it's been the maths bit to work out the enclosure size that put me off as no good at maths

↑ In prime. Once I decide what to do with the ornamental panel on the front, the screw holes will be filled and covered over. The panel could be raised ½" or so to add LEDs behind it or it could be laminated to add strength.

Next will be a line for a GTO 8 that I have laying around. I'll probably use it for a computer sub but I might sell it. Then, when the SA-15 I ordered comes in, a line for it. If it works out well, I'll sell it, remove the seat from my truck and put two X-15s in a permanently mounted t-line.

Re: JBL GTO 10 in ¼ Wave T-Line

Originally Posted by Caveivian

It would have to be for a pair of epic 8's. Design and build me one.

If you mean these little beasts, that will be an almost 12' line and it'll be just a little bit more line area than the one above. Those would probably do a lot better on the lows than the one above also.

Give me dimensions of where it's going and tell me how you want it finished and I'll get you a price.

Re: JBL GTO 10 in ¼ Wave T-Line

Here's the next t-line I'm trying in the truck. It will have a Sundown SA-15 in it and I'll probably end up taking the rear seat out and building a line for two X-15s.

I tried to do more progress pictures for those who want to see how these things go together. This line is identical to the first one, expect of course, for the size.

I actually finished it, less the second layer of baffle, and got it in the truck for testing. But... the only thing I had to test it with was a Skar IVX-15 and it did okay for what it is. Honestly, that little JBL ten can handle a lot more power than the Skar woofer can, so I could only test with it wired to 4Ω, which means 500 watts on my amp.